This chapter discusses the characterization techniques subscribe to the device-independent paradigm and, as such, involve deriving transformations between device-dependent and colorimetric representations. It deals with a description of some fundamental concepts and provides a more detailed exposition of characterization techniques for commonly encountered input and output devices. The spectral characteristics of the sensors have profound implications on input device characterization. The generation and measurement of color targets is an important component of device characterization. Traditionally, the printing industry has satisfactorily relied on densitometers to make color measurements of prints made by offset ink. However, given the larger variety of colorants, printing technologies, and viewing conditions likely to be encountered in digital color imaging business, the use of spectral measurement instruments is strongly recommended for device characterization. With input device characterization, neither the captured device values nor the measured device-independent values of the color target can be guaranteed to lie on a regular lattice.